This invention relates generally to electric energy conversion, and, more specifically, to efficient connection of a photovoltaic module to a power grid or a load.
With the rising cost and scarcity of conventional energy sources and concerns about the environment, there is a significant interest in alternative energy sources such as solar power and wind power. Solar power generation uses photovoltaic (PV) modules to generate electricity from the sun. Multiple PV cells are connected electrically to one another in such systems. The electricity generated by PV modules is transmitted to the power grid through one or multiple power electronic converters such as diode clamped converters.
In general, the efficiency of power electronic converters used in photovoltaic systems is poor at partial load and high at medium to full load. Since the converters operate at partial load most of the time, overall efficiency of the PV systems is less than optimal. Hence, power losses of diode clamped multilevel converters are an important issue in unit sizing photovoltaic systems because of the influence of such losses on the total energy delivered to the load. Power losses occur in diode clamped converters mainly because of losses in switching devices such as Insulated Gate Bipolar Transistors (IGBTs), Gate Turn Off (GTO) Thyristors, Integrated Gate Commuted Thyristors (IGCTs) and diodes which are generally used in the converters or passive components such as filter inductors. The switching devices generally have three major types of losses: conduction losses, switching losses, and gate drive losses. Gate drive losses are not present in diodes. However, conduction losses and switching losses are very much part of the diode losses. Losses in fast switching diodes are typically higher than slow switching diodes. The switching losses correspond to the losses that occur during state changes of the switching device (during turn on and turn off). The conduction losses correspond to losses that occur in the switching device during its conduction (when the device is carrying a current). Gate drive losses refer to the energy required to charge and discharge gate-source and gate-drain capacitances of the switching devices and are affected by switching frequency, drain-source capacitance, and the voltage traversed. Filter inductor losses consist typically of copper and iron losses. Copper losses in power converters are typically increased by skin and proximity effects. Therefore, it is desirable to determine a method and a system that will address the foregoing issues.